This application claims the benefit of Korean Application No. 2001-669, filed Jan. 5, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a polymeric gel electrolyte and a lithium battery using the same, and more particularly, to a polymeric gel electrolyte formed by polymerization used in a battery, a method of manufacturing the polymeric gel electrolyte, a lithium battery having improved high-rate charging/discharging characteristics using a separator containing the polymeric gel electrolyte, and a method of manufacturing the lithium battery.
2. Description of the Related Art
Conventional lithium secondary batteries use electrolytes, such as liquid electrolytes or solid electrolytes, and in particular, polymeric electrolytes. Since a lithium secondary battery using a polymeric electrolyte is unlikely to damage equipment due to leakage of an electrolyte solution and the electrolyte itself serves as a separator, the polymeric electrolyte allows for miniaturization of the battery and realizing a high energy density battery. Owing to such advantages, much attention has been paid to lithium secondary batteries using polymeric electrolytes that can be used, for example, in operating power sources such as those used in portable electronic devices and computer memory backups.
An example of a lithium secondary battery using the polymer electrolyte as the separator is described, for example, in U.S. Pat. No. 5,952,126. In this battery, a polymeric electrolyte comprises a polymer matrix composed of a copolymer of N-isopropylacryl amide and polyethyleneglycol dimethacrylate and an electrolyte solution. The polymer matrix and the electrolyte solution are made into a film that is interposed between a cathode and an anode. The composition which forms the polymer matrix can also include polyethylene glycol and/or dimethacrylate, which are added during the manufacture of the electrodes.
However, the above-described lithium secondary battery is difficult to manufacture. Also, due to a low content of the electrolyte solution, the ion conductivity between the cathode and the anode deteriorates, which adversely affects the battery performance. More specifically, the battery has a poor capacity in view of the high-rate charging/discharging characteristics.
It is an object of the present invention to both provide a polymeric gel electrolyte having excellent mechanical strength and improved ion conductivity between electrodes with an increased amount of an electrolyte solution, and a method of manufacturing the polymeric gel electrolyte.
It is an additional object of the present invention to both provide a lithium battery having improved high-rate charging/discharging characteristics by using the polymeric gel electrolyte, and a method of manufacturing the lithium battery.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects, a polymeric gel electrolyte polymeric gel electrolyte prepared by polymerizing a polymer electrolyte precursor according to an embodiment of the present invention includes a polymer represented by formula 1, a crosslinking agent represented by formula 2, and an electrolyte solution composed of a lithium salt and a non-aqueous organic solvent, where: 
x ranges from 0.1 to 0.6 mol, y ranges from 0.1 to 0.8 mol, z ranges from 0.1 to 0.8 mol, R is an alkyl having 1 to 6 carbon atoms, n is an integer from 3 to 30, and Rxe2x80x2 is hydrogen or CH3.
According to another embodiment of the present invention, a method of manufacturing a polymeric gel electrolyte includes preparing a polymer electrolyte precursor by mixing a polymer represented by formula 1, a crosslinking agent represented by formula 2, and an electrolyte solution composed of a lithium salt and a non-aqueous organic solvent, where: 
x ranges from 0.1 to 0.6 mol, y ranges from 0.1 to 0.8 mol, z ranges from 0.1 to 0.8 mol, R is an alkyl having 1 to 6 carbon atoms, n is an integer from 3 to 30, and Rxe2x80x2 is hydrogen or CH3; and polymerizing the polymer electrolyte precursor.
According to a further embodiment of the present invention, a lithium battery includes a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is an insulating resin sheet having a network structure to contain a polymeric gel electrolyte, the polymer electrolyte being prepared by polymerizing a polymer electrolyte precursor comprising a polymer represented by formula 1, a crosslinking agent represented by formula 2, and an electrolyte solution composed of a lithium salt and a non-aqueous organic solvent, where: 
x ranges from 0.1 to 0.6 mol, y ranges from 0.1 to 0.8 mol, z ranges from 0.1 to 0.8 mol, R is an alkyl having 1 to 6 carbon atoms, n is an integer from 3 to 30, and Rxe2x80x2 is hydrogen or CH3.
According to yet another embodiment of the present invention, a method of manufacturing a lithium battery includes inserting an insulating resin sheet having a network structure between a cathode and an anode to form an electrode assembly and accommodating the electrode assembly into a battery case, injecting a polymer electrolyte precursor comprising a polymer represented by formula 1, a crosslinking agent represented by formula 2, and an electrolyte solution composed of a lithium salt and a non-aqueous organic solvent, into the battery case having the electrode assembly to impregnate the polymer electrolyte precursor into the insulating resin sheet having the network structure, where: 
x ranges from 0.1 to 0.6 mol, y ranges from 0.1 to 0.8 mol, z ranges from 0.1 to 0.8 mol, R is an alkyl having 1 to 6 carbon atoms, n is an integer from 3 to 30, and Rxe2x80x2 is hydrogen or CH3, and polymerizing the resultant of the injected polymer electrolyte precursor to form the polymeric gel electrolyte.
According to an aspect of the invention, the polymer represented by formula 1 has a weight-average molecular weight of 5,000 to 2,000,000 and a content thereof is 2 to 10 parts by weight based on 100 parts by weight of the polymer electrolyte precursor.
According to another aspect of the invention, the crosslinking agent represented by formula 2 has a weight-average molecular weight of 258 to 500,000, and a content thereof is 0.01 to 50 parts by weight based on 100 parts by weight of the polymer electrolyte precursor.
According to still another aspect of the invention, the polymer electrolyte precursor further includes as an additional crosslinking agent 0.01 to 50 parts by weight of N,N-(1,4-phenylene)bismaleimide, based on 100 parts by weight of the polymer electrolyte precursor.
According to yet still another aspect of the invention, the non-aqueous organic solvent is at least one selected from the group consisting of propylene carbonate, ethylene carbonate, dimethylcarbonate, methylethylcarbonate, diethylcarbonate and vinylene carbonate, and the lithium salt is at least one selected from the group consisting of LiClO4, LiBF4, LiPF6, LiCF3SO3, and LiN(CF3SO2)2.
According to a further aspect of the invention, the content of the electrolyte solution is in the range of 40 to 98 parts by weight based on 100 parts by weight of the polymer electrolyte precursor.
According to a still further aspect of the invention, the insulating resin sheet is one of a polyethylene resin, a polypropylene resin or a combination thereof, has a porosity of 40 to 80%, and has a thickness in the range of 10 to 30 xcexcm.
According to a yet further aspect of the invention, in preparing the polymer electrolyte and lithium battery, the polymerization temperature is in the range of 60xc2x0 C. to 100xc2x0 C.